Auto cure variable fan drive control system and associated methods

ABSTRACT

Methods and systems for controlling air characteristics for storage facilities. A controller and temperature sensors can detect an external temperature and compare it to a reference temperature. Depending on the relationship between the external temperature and the reference temperature (e.g. warmer or colder) the controller can initiate a burner, open an air intake, and operate fans to achieve desirable conditions within the facility efficiently.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional Application No. 61/346,105, filed May 19, 2010, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The following disclosure relates generally to devices, systems and methods for controlling air characteristics in crop storage facilities.

BACKGROUND

Crops such as onions, garlic, tulip bulbs, and other, similar goods are sensitive to their surroundings and must be cured between harvesting and consumption. Controlling the air quality, temperature, humidity, and other parameters in facilities where these crops are stored requires energy. Accordingly, efficient methods for preserving crops without sacrificing revenue are important to farmers and companies. Daily temperature variation can limit the efficiency of many conventional crop storage systems, particularly in dry, desert areas such as the southwestern United States where the temperature variation is extreme. One approach has been to heat air as it enters a storage facility. Doing so is expensive and without proper controls can be inefficient and can even harm the stored crop. Also, despite the increasing size of burners used at such facilities, frequently the temperature drop is too great for even the largest and most sophisticated burners to handle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic illustration of a storage facility and a system for controlling the interior air characteristics within the storage facility in accordance with some embodiments of the present disclosure.

FIG. 2 is a block diagram illustrating a method for controlling the internal air characteristics of a storage facility in accordance with several embodiments of the present disclosure.

FIG. 3 is a block diagram illustrating a method for controlling the internal air characteristics of a storage facility in accordance with selected embodiments of the present disclosure.

FIG. 4 is a block diagram illustrating a method for controlling the internal air characteristics of a storage facility in accordance with several embodiments of the present disclosure.

FIG. 5 is a block diagram illustrating a method for controlling the internal air characteristics of a storage facility in accordance with several embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is directed generally to apparatuses, devices and associated methods for controlling interior air characteristics of a storage facility.

Several details describing structures and processes that are well-known and often associated with storage facilities and air handling equipment are not set forth in the following description to avoid unnecessarily obscuring embodiments of the disclosure. Moreover, although the following disclosure sets forth several embodiments of the invention, other embodiments can have different configurations, arrangements, and/or components than those described herein without departing from the spirit or scope of the present disclosure. For example, other embodiments may have additional elements, or they may lack one or more of the elements described below with reference to FIGS. 1-5.

Throughout this discussion, reference will be made to onions as a crop to be cured and treated by the disclosed systems and methods for conciseness and clarity. It will be appreciated, however, that any other crop can be cured and treated by the disclosed systems and methods. Garlic, tulip bulbs, and other bulb crops, for example, are generally similar to onions, but the disclosed methods and systems can be used with any other crop.

FIG. 1 is a partially schematic illustration of a storage facility 100 according to several embodiments of the disclosure. The storage facility 100 can contain goods 110, such as onions, potatoes, and/or other types of crops or other products. The storage facility 100 can be part of a series of similar storages, or can be a stand-alone unit. The storage facility 100 can have virtually any suitable size to meet the needs of a particular farmer or storage company. The goods 110 can be loosely stored in the storage facility 100 or can be in individual packaging or crates.

After harvesting or collecting the goods 110, the goods 110 may require a period of time for curing during which environmental conditions in the storage facility 100 can be controlled. In one aspect of this embodiment, the storage facility 100 can include an air control system 105 that uses air from outside the storage facility 100 to achieve a desired temperature and humidity within the storage facility 100. The air control system 105 can include an air intake 120, a fan 130, and a burner 140. In some embodiments, the fan 130 includes a 10-30 horsepower propeller-type ventilation fan, and the burner 140 includes a vane-axial combustion heater. Other types of fans and burners can be used as well. Air flows through the intake 120, the fan 130, and the burner 140 from outside the storage facility 100 until it reaches the goods 110. The air can travel along a plenum 150 which can include several pipes, ducts, and other passageways. The plenum 150 generally describes mechanisms through which the air travels, and as such the plenum 150 can have virtually any suitable layout and configuration. Intake 120 can include one or more intake ports placed around the storage facility 100. A corresponding air outlet 152 can be operated analogously to the intake 120 to ensure the conditioned air is distributed throughout the storage facility 100. Similarly, the intake 120, fans 130, and burner 140 can include multiple units arranged advantageously around the storage facility 100. For purposes of illustration and ease of reference, however, FIG. 1 depicts a simplified, schematic view of these components.

In some embodiments, a controller 160 is connected to the intake 120, the fans 130, and the burner 140. The controller 160 can be local to the storage facility 100 or it can be located remotely and can communicate with the storage facility 100 (or with several, distributed storages 100). The controller 160 can be controlled through a remote management system as discloses in U.S. Provisional Patent Application No. 61/235,663, entitled Remote Management of Storage Facilities, which is hereby incorporated by reference. A series of sensors 170 can be disposed throughout the storage facility 100 and outside of the storage facility 100 to gather data such as temperature, humidity, time, and other parameters. The sensors 170 can communicate with the controller 160 to provide the controller 160 with data to operate the storage facility 100.

The storage facility 100 can operate to cure the goods 110 by maintaining a desired air temperature and air intake to the storage facility 100. Some curing and/or storage operations are more favorably achieved by a high air throughput and relatively warm temperatures. For example, a storage facility 100 used to cure and dry onions, garlic, tulips, or other bulb crops benefit from a relatively large amount of air throughput and at comparatively high temperatures. Other storage facilities 100 used for other types of goods 110 may thrive in different conditions. Accordingly, depending on the needs and character of the goods 110, a preferred interior temperature is reached and the intake 120 is fully open to admit the maximum amount of exterior air to the storage facility 100. The intake 120 can be opened and closed in degrees to change the amount of air admitted to the storage facility 100, and the burner 130 can be used at different levels to increase the temperature within the storage facility 100 when the outside air is warmer or colder than a desired interior temperature. In some embodiments, the fans 130 comprise variable frequency drives (VFD) that can alter the throughput of the fans 130 with great accuracy and reliability. The controller 160 can manage these variables in this instance.

The controller 160 can comprise a programmable logic controller (PLC) or other microprocessor-based industrial control system that communicates with components of the storage facility 100 through data and/or signal links to control switching tasks, machine timing, process controls, data manipulation, etc. In this regard, the controller 160 can include one or more processors that operate in accordance with computer-executable instructions stored or distributed on computer-readable media. The computer-readable media can include magnetic and optically readable and removable computer discs, firmware such as chips (e.g., EEPROM chips), magnetic cassettes, tape drives, RAMs, ROMs, etc. Indeed, any medium for storing or transmitting computer-readable instructions and data may be employed. The controller 160 and embodiments thereof can be embodied in a special purpose computer or data processor that is specifically programmed, configured or constructed to perform one or more of the machine operations explained in detail below. Those of ordinary skill in the relevant art will appreciate, however, that the storage facility 100 and components such as the intake 120, the fans 130, and the burner 140 can be controlled with other types of processing devices including, for example, multi-processor systems, microprocessor-based or programmable consumer electronics, network computers, and the like. Data structures and transmission of data and/or signals particular to various aspects of the controller 160 are also encompassed within the scope of the present disclosure.

FIG. 2 is a block diagram illustrating a method 200 for controlling air characteristics within a storage facility 100 according to several embodiments of the present disclosure in which the general trend in temperature is from high to low (e.g., at nightfall). The method 200 can be carried out by the system 105, defined generally as the components of the storage facility 100 that control the conditions (e.g., the air and temperature conditions) within the storage facility 100.

An initial condition 210 according to some embodiments is defined by an outside air temperature that is above a desired interior air temperature, such that the intake 120 is fully open and the maximum amount of air is entering the storage facility 100. As noted above, a storage facility 100 used for bulb products generally uses a large amount of air at a high temperature to cure and store the bulb products. Other stored goods 110 have different desirable conditions, and parameters of this disclose can be adjusted accordingly. In the initial condition 210, the fan 130 operates at a high or maximum level, and the burner 130 is not in use. The temperature in the air plenum 150 is periodically measured 220. (The temperature can be measured at various locations within the storage facility 100, including the plenum 150.) If the temperature is at or above a threshold temperature, T, the method includes waiting a predetermined period of time before checking the temperature again 220. In an example, T can be 70° Fahrenheit. If the temperature is below T, the system 105 determines 230 whether the burner 140 is operating at the high or maximum level. If the burner 140 is not operating at all, or is operating at a level below the high or maximum level, the burner 140 can be turned up 240. Control then passes to measuring the temperature 220 until the temperature in the plenum 150 drops below T again.

If the burner 140 is operating at the maximum available level, the system 205 determines 250 whether the fans 130 are operating at their minimum level. The minimum level for the fans 130 can be where the fans are operating at a low level, or can be where the fans 130 are not operating at all. If the fans 130 are not at their lowest level, the fans 130 can be reduced 260. Because the volume of air passing through the fans 130 is generally directly proportional to the energy required to heat the air by a specific amount, reducing the air can have the effect of increasing the temperature in the plenum 150 and in the storage facility 100. This allows for curing the goods 110 more efficiently despite colder, less favorable outside conditions. If the fans 130 have reached their minimum level, the intake 120 position can be determined 270.

If the intake 120 is open, the intake 120 can be stepped 280 toward a closed position. In some embodiments, the intake 120 is a door or set of doors that can move between several positions between open and closed to vary the size of the air passage and hence the air throughput. The doors can be operated by actuators such as pneumatic, hydraulic, or mechanical means. Closing the intake 120 can further reduce the throughput of air in the storage facility 100, which in turn increases the temperature in the plenum. Similarly to slowing the fans 130, this allows for effective curing despite unfavorable conditions outside the storage facility 100. Once the doors are closed completely, the system 105 enters a recirculation phase 190 in which the air within the storage facility 100 is recirculated throughout the storage facility to continue curing to a reduced extent while the conditions outside the storage facility 100 are undesirable. This helps to maintain the temperature within the storage facility 100 at a level at which the goods 110 can continue to cure until conditions outside improve.

In some embodiments, the changing conditions outside of the storage facility 100 are caused by nightfall. During a typical day the temperature will drop at sunset and rise at dawn. The sensors 170 can detect this temperature drop and communicate with the controller 160 to initiate the method 200 described above. In some embodiments, this process depends upon temperature and not upon time of day. This allows the central system 105 to be sensitive to temperature fluctuations caused by weather. A delay between temperature readings can help to make the system 105 immune to “noise.” For example, if a short-lived rain or wind causes the temperature to drop for less time than the duration of the delay (e.g., five minutes, ten minutes, etc.), the storage facility 100 can ignore these changes and continue operation. However, if a storm lasts long enough to affect the interior temperature, such as the temperature in the plenum 150, the controller 160 can react and execute the method 200 described above. This creates more efficient use of ambient temperature for curing or storage of goods 110.

FIG. 3 is a block diagram depicting a method 300 for controlling interior air characteristics of a storage facility 100 in accordance with another embodiment of the present disclosure. Similar to the method 200 discussed above and shown in FIG. 2, the method 300 is for use generally when the temperature trend is high to low. An initial condition 305 can be generally similar to the initial condition 210 described above with reference to FIG. 2. In particular, the intake 120 is fully open, the fans 130 are operating at their maximum capacity, and the burner 140 is not in use. Next, the sensors 170 can measure the temperature in the plenum 150 and in other locations within the storage facility 100, and determine 310 whether the temperature is below a threshold temperature, T. If so, the burner condition can be determined 315 and increased 320 if not operating at maximum capacity. After a predetermined period of time, (e.g., five minutes, ten minutes, etc.) the temperature can be determined 310 again. After increasing the burner 140 the temperature will likely rise or at least maintain a steady level for a period of time.

If the temperature is not less than the predetermined threshold temperature, T, a second temperature inquiry can determine 325 whether the temperature has risen by more than a predetermined temperature difference, A, above the temperature T. In some embodiments, this predetermined temperature difference A is 5° Fahrenheit, or about 5° F. If not, the system 105 can wait 330 and then return to compare 310 the temperature in the storage facility 100 to the threshold temperature, T. If, however, the temperature in the storage facility 100 has increased by more than A, the system 105 can reverse 335. Specific examples of the reverse operation will be given below with reference to FIG. 4.

The method 300 continues when the burner 130 is operating at a maximum level by determining 340 whether the fans 130 are operating at their lowest setting. If not, the speed of the fans 130 can be decremented 345. As discussed above, reducing the speed of the fans 130 can increase the temperature in the storage facility 100 to continue curing or treating the goods 110 even when the outside temperature is not ideal. After decrementing the speed of the fans 130, the temperature is again compared 350 to the threshold temperature, T. If the temperature is not below T, the temperature can be measured 355 for an increase of greater than A. If the temperature has risen greater than A, the method 300 will reverse 335; otherwise, the system 105 waits 360 for a predetermined period before comparing the temperature in the storage facility 100 to the threshold temperature, T.

Once the fans 130 reach the minimum operating level, the intake 120 condition is assessed 365. If the intake 120 is open, the intake 120 can be stepped toward the closed position 370. After at least partially closing the intake 120, the temperature in the storage facility 100 can again be compared against the threshold temperature, T. If the temperature is still below T the intake 120 can be assessed 365 and stepped toward the closed position 370 again. If the temperature in the storage facility 100 is not below T, the system 105 can determine 380 whether the temperature has risen by more than a predetermined amount, A. If so, the system 105 can reverse 335; otherwise, the system 105 waits before returning to measuring the temperature in the storage facility 100 again. Once the intake 120 is fully closed, the system 105 can enter a recirculation phase 390 similar to the recirculation phase 290 described above with reference to FIG. 2.

The method 300 includes three generally analogous stages in which the temperature is compared to a reference temperature, T, and an action is taken to maintain a given temperature in the storage facility 100. In several embodiments, the stages are 1) increasing the burner 140, 2) decreasing the fans 130, and 3) closing the doors. Between each step the temperature is measured and further incremental steps are performed. If the temperature increases beyond a set range, the operation can reverse to lower the temperature. Although the method 300 depicted in FIG. 3 shows these three stages occurring sequentially, other embodiments can include performing two or more of these stages simultaneously, or performing these stages in other sequences, and/or omitting one of these stages. For example, if the temperature is determined to be below the threshold temperature, T, the burner 140 can be increased and the fans 130 can be decremented before measuring the temperature again. Alternatively, the fans 130 and the intake 120 can be decremented jointly without necessarily measuring the temperature between increments.

FIG. 4 illustrates a method 400 for controlling interior air characteristics of a storage facility 100 in accordance with another embodiment of the present disclosure. The method 400 is generally for use when the temperature trend is from low to high (e.g., at dawn). When moving from cold to warm temperatures, an initial condition 405 can include a recirculation phase described above with reference to FIGS. 2 and 3, where the intake 120 (and corresponding outlet) is closed and air is moved throughout the storage facility 100 to a limited degree. The central system 105 can measure 410 the external temperature periodically and compare it to a temperature at which the initial condition 405 was reached. For example, the external temperature can be measured when the intake 120 is fully closed and the storage facility 100 enters a recirculation phase. If the temperature outside the storage facility 100 has risen by more than a threshold amount (e.g., 5° or 10° after a predetermined amount of time 415 (e.g., five or ten minutes), the method 400 can begin 420. (In some embodiments, the method 400 can begin when the system 105 reverses according to the method 300 described above with reference to FIG. 3.) At this point, the burner 140 can be turned on and operated at a high or maximum level. The temperature in the plenum 150 or elsewhere within the storage facility 100 can be measured and compared 425 to a reference temperature, T. If the temperature is less than or equal to T, the system 105 can wait 430 a set amount of time. If the reference temperature, T, is exceeded, the system 105 can step open 435 the intake 120 and increase 440 the fan 130. While the fan 130 is operating below a maximum level and while the intake 120 is partially closed, the system 105 can continue the loop. Once the fan 130 reaches the maximum level and the intake is fully open, any further increase in exterior air temperature will be reflected in an increase in interior air temperature.

With the burner 140 and fans 130 operating at maximum and the intake 120 fully open, the temperature in the plenum 150 can be measured and compared to a desired reference temperature. Until this temperature is exceeded, the system 105 can wait 455 between measurements. If the temperature is above the desired reference temperature, the operational status of the burner 140 can be assessed 460, and if the burner 140 is still running, it can be turned down 465. Once the burner is off, the system 105 can stop 470. In this state, the intake air is warm enough that the desired curing/storage temperature is reached within the storage facility 100 without using the burner, with the intake 120 fully open, and with the fans 130 operating at maximum. This condition is similar to the initial conditions 210, 305 described with reference to FIGS. 2 and 3. Accordingly, the system 105 is ready to perform the methods 200, 300 described for when the temperature trend is generally from high to low.

The method 400 described here includes incrementing 435 the intake 120 and incrementing the fan 130 simultaneously between measurements. It is to be appreciated that any incrementing or decrementing step described in any of FIGS. 2-4 can be performed sequentially or serially with other incrementing or decrementing steps. Temperature measurements can be taken at any point during the methods 200, 300, 400, and can also be taken substantially continuously throughout the methods.

FIG. 5 illustrates yet another method 500 according to several embodiments of the present disclosure in which a storage facility can recirculate air while outside ambient temperatures remain cold, but can detect when the outside air has warmed and then use the warm outside air within the facility. In an embodiment, the method 500 can be appended to the block diagram of FIG. 3. In particular, the method 500 can be a continuation of a recirculation operation 390 shown and described in FIG. 3. The method 500 can also be used in other conditions that begin with a recirculation operation 510. Recirculating air within a storage facility can be performed when ambient temperatures are below a predetermined threshold at which equipment at the storage facility, such as a burner, a VFD, etc., cannot achieve desired minimum temperature within the facility using ambient air as an input. The temperature outside the facility will inevitably change, however, and eventually the air will warm to a degree that the air can be used within the facility. For example, overnight temperatures may be too low, but at dawn the temperature may rise above acceptable levels. When the recirculation operation 510 begins, the ambient temperature can be recorded in memory as “R temp.” Periodically, this temperature can be compared 520 to the current ambient temperature, and if the ambient temperature has risen above R temp by a predetermined amount (e.g., 5° F.), certain steps can be executed 530 to intake this air.

Before determining that the outside temperature has reached a sufficiently high temperature, the method 500 can require that a predetermined time period elapses during which the outside temperature is higher than R temp. For example, the method 500 can include comparing the two temperatures and marking a first time at which the temperature threshold is reached and waiting a predetermined time (e.g., 999 seconds) before comparing the temperatures again. If the outside temperature is still above the threshold temperature the method 500 can include proceeding with further steps. If the temperature rises above the threshold for less than the predetermined time period, the period can reset and continue to monitor the temperature difference. Comparing the temperatures 520 can include taking many measurements during the time period and if a sufficient number or percentage of the measurements are above the threshold, the method 500 can proceed.

In some embodiments, a VFD can be turned on to a minimum fan speed, the doors can be opened, and a burner can be turned on. In some instances, the burner can be turned on to a maximum level at this stage because the outside air may be expected to be relatively cold. After another period elapses, the temperature in the plenum can be measured 540 to determine whether the situation is stable by measuring the temperature in the plenum. If not (e.g., if the ambient air is still too cold to maintain desired conditions within the facility), the method 500 can include several operations to verify that the temperature in the plenum cannot be maintained, and that no transient effects are causing the low temperature. For example, the method 500 can include checking whether the burner is operating at a maximum level 550. If not, the burner can be incremented 530 and the temperature in the plenum can be measured again 540. If the burner is operating at a maximum temperature, a timer 560 can start. The timer 560 can be set to any suitable duration depending on the application and circumstances. Where transient conditions are expected, the timer can be longer to allow the transient effects to subside without affecting the method 500. In contrast, where interruptions and other transient effects are not expected, the timer can be shorter. In some embodiments, the timer can be set to between two and sixteen minutes. When the timer expires, the recirculation operation 510 can resume. If the plenum temperature is maintained 540, the VFD can be incremented or decremented, the door opened or shut, and the burner can be decremented or incremented 580. These variables can each be adjusted bi-directionally depending on the temperature of the air in the plenum. For instance, if the air is too cold the VFD can be decremented, the door can be shut, and the burner incremented; if the air is too warm the VFD can be incremented, the door opened, and the burner decremented. After each incremental adjustment to the VFD, the doors, and the burner, the method can include determining 590 whether the VFD is at a maximum speed, the door is fully open, or the burner is off. Once all these variables reach a maximum state the method 500 can terminate 600 and/or pass control to another routine.

The incrementing and decrementing actions described with reference to FIGS. 2-5 can include steps of equal or unequal distance as measured by time spacing between actions, temperature interval, or flow volume change per step. In some embodiments, for example, the size of the steps is proportional to a temperature difference between the interior temperature and the predetermined threshold temperature. The system 105 can operate in a variety of conditions and is sensitive to temperature variation caused by daily temperature changes and by other events such as a rainstorm or wind, etc.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the various embodiments of the invention. Further, while various advantages associated with certain embodiments of the invention have been described above in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. The following examples are directed to additional embodiments of the disclosure. 

1. A method for controlling interior air temperature inside a crop storage facility, wherein a fan moves heated air from a burner in the storage facility and can draw air into the storage facility through an air intake, the method comprising: detecting a first temperature of air inside the storage facility; comparing the first temperature to a second temperature; if the first temperature is less than the second temperature, increasing an operating level of the burner; if the first temperature is less than the second temperature and the burner level is at a predetermined maximum operating level, decreasing a fan output; if the first temperature is less than the second temperature and the fan throughput is at a predetermined minimum level and the burner is at or above a predetermined maximum, at least partially closing the air intake; and if the first temperature is less than the second temperature, the burner is at the predetermined maximum operating level, and the air intake is fully closed, recirculating the air inside the storage facility.
 2. The method of claim 1, further comprising controlling the fan output with a variable frequency drive.
 3. The method of claim 1 wherein comparing the first temperature to the second temperature comprises comparing the first temperature to the second temperature at predefined time intervals.
 4. The method of claim 3 wherein the predefined time intervals are between five and ten minutes.
 5. The method of claim 1, further comprising if the air intake is closed, periodically comparing temperature outside the facility to a predefined temperature.
 6. The method of claim 1, further comprising: after fully closing the air intake, periodically comparing the temperature outside the facility to a predefined temperature; if the temperature outside the facility is greater than the predefined temperature, opening the air intake and increasing the fan output at each periodic comparison between the temperature outside the facility and the predefined temperature; and if the air intake reaches a maximum open status, decrementing the burner operating level.
 7. A method for controlling air temperature in a crop storage facility, the method comprising: monitoring an external temperature; comparing the external temperature to a first reference temperature; if the external temperature is greater than the first reference temperature, opening an air intake door to the facility to permit external air to enter the facility and operating a burner at a first level; with the air intake door open, monitoring a temperature within an air plenum of the facility; if the temperature in the air plenum is below a second reference temperature, closing the air intake door and turning off the burner; and if the temperature in the air plenum is above the second reference temperature, opening the air intake door.
 8. The method of claim 7, further comprising if the temperature in the air plenum is above the second reference temperature, reducing the level of the burner.
 9. The method of claim 7 wherein opening an air intake door comprises operating a variable frequency drive fan.
 10. The method of claim 7 wherein monitoring the external temperature and comparing the external temperature to the first reference temperature is performed by a controller.
 11. The method of claim 7 wherein the storage facility contains perishable goods, and wherein the first reference temperature and the second reference temperature are dependent upon desirable conditions for the perishable goods.
 12. The method of claim 11 wherein the perishable goods are at least one of onions or potatoes.
 13. The method of claim 7 wherein monitoring the temperature within the air plenum comprises operating a plurality of sensors within the air plenum to detect temperature at a plurality of locations within the air plenum.
 14. The method of claim 13 wherein monitoring the temperature within the air plenum comprises averaging the temperature from the plurality of sensors.
 15. The method of claim 7 wherein initiating a burner at a high level comprises initiating the burner at a maximum level.
 16. A method for operating an air control system of a facility in a warm-to-cold operation, the air control having a burner, at least one fan, and an air intake, wherein the air control system is reversible between the warm-to-cold operation and a cold-to-warm operation, the method comprising: operating the air control system in a warm-to-cold operation; comparing an interior air temperature of the facility to a reference temperature; if the interior air temperature is greater than the reference temperature, reversing the air control system from the warm-to-cold operation to the cold-to-warm operation; if the interior air temperature is less than the reference temperature, increasing the burner; if the burner has reached a maximum operating state, and the interior air temperature is greater than the reference temperature, reversing the air control system from the warm-to-cold operation to the cold-to-warm operation; if the burner has reached a maximum operating state and the interior air temperature is less than the reference temperature, reducing the fan; if the fan has reached a minimum operating state, and the interior air temperature is greater than the reference temperature, reversing the air control system from the warm-to-cold operation to the warm-to-cold operation; if the fan has reached a minimum operating state, and the interior air temperature is less than the reference temperature, at least partially closing the air intake; and if the air intake is closed, entering a recirculation operation.
 17. The method of claim 16, further comprising recording an external temperature when entering the recirculation operation, and using the recorded external temperature as the reference temperature.
 18. The method of claim 16 wherein the recirculation operation comprises an air treatment process using a closed circuit of air within the facility.
 19. The method of claim 16, further comprising comparing the interior air temperature to the reference temperature and identifying a difference between the interior air temperature and the reference number, the difference having a magnitude.
 20. The method of claim 19 wherein reducing the fan comprises reducing the fan by an amount dependent upon the magnitude of the difference.
 21. The method of claim 19 wherein increasing the burner comprises increasing the burner by an amount dependent upon the magnitude of the difference.
 22. The method of claim 19 wherein closing the air intake comprises closing the air intake by an amount dependent upon the magnitude of the difference. 